8.04: impossible to enable eth0

[flapane]

Athlon xp box updated to gutsy i386 2 days ago.
Setting a network interface with my isp is very simple: use dhcp.
It worked well until this afternoon.
After a shutdown, eth0 won't work. If I go in kcontrol, and try to enable it, sometime it says something that in english should be: Can't process XML output of network interface.
Some other times it doesn't happen nothing, and if you click on ENABLE, the button always goes on DISABLED.
ifconfig eth0 up from shell leads to nothing.

If I boot from a livecd, it works well, so we should exclude any phisical damage.

[yoyoned]

try sudo dhclient from the terminal. If that doesn't work, post any error messages you get.

[flapane]

It works, and /etc/network/interfaces is set, too.
Anyway after a reboot, the problem still happens